Semiconductor memory device

ABSTRACT

A semiconductor memory device that includes an input buffer being inputted a write data from outside to buffer the write data and a control circuit putting the input buffer into an inactive state during a read operation and putting the input buffer into an active state when a read mask signal is inputted thereafter is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2004-250631, filed on Aug. 30,2004, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory device.

2. Description of the Related Art

In Japanese Patent Application Laid-Open No. Hei 9-320258 (PatentDocument 1), there is disclosed a SDRAM that includes plural data masksignal terminals provided to correspond to data input and outputterminals, and input control circuits and output control circuitscapable of controlling data input and output from the corresponding datainput and output terminals in response to the logic of signals given toindividual data mask signal terminals from outside.

In the U.S. Pat. No. 6,466,492 (Japanese Patent Application Laid-OpenNo. 2002-74952) (Patent Document 2), there is disclosed a semiconductormemory device in which an input buffer is activated/inactivated by asynchronizing mask control signal when it is in an active state.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide alow-current-consumption semiconductor memory device.

According to one aspect of the present invention, a semiconductor memorydevice that includes an input buffer being inputted a write data fromoutside to buffer the write data and a control circuit putting the inputbuffer into an inactive state during a read operation and putting theinput buffer into an active state when a read data mask signal isinputted thereafter is provided.

According to another aspect of the present invention, a semiconductormemory device that includes a control circuit putting a clock signal forlatch into an inactive state during a read operation and putting theclock signal for latch into an active state when a read data mask signalis inputted thereafter and a latch circuit to latch a write datainputted from outside in synchronization with the clock signal for latchis provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration example of asemiconductor memory device according to one embodiment of the presentinvention;

FIG. 2 is a circuit diagram showing a configuration example of a circuit104 in FIG. 1;

FIG. 3 is a timing chart showing an example of a read operation of thecircuit in FIG. 2;

FIG. 4 is a timing chart showing an example of a writeinterruptoperation during a burst read of the circuit in FIG. 2;

FIG. 5 is a circuit diagram showing a configuration example of a circuit104 in FIG. 1 according to one embodiment of the present invention;

FIG. 6 is a timing chart showing an example of a read operation of thecircuit in FIG. 5; and

FIG. 7 is a timing chart showing an example of a writeinterruptoperation during a burst read of the circuit in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram showing a configuration example of asemiconductor memory device according to the present invention.Descriptions will be given by citing a SDRAM (Synchronous Dynamic RandomAccess Memory) as one example of the semiconductor memory device.

A semiconductor memory device 100 has, as outside terminals 110,respective terminals for a clock enable signal CKE, a clock signal CLK,a chip select signal /CS, a row address strobe signal /RAS, a columnaddress strobe signal /CAS, a write enable signal /WE, a two bits ofbank address BA, a 12 bits of address A, a two bits of data mask signalDQM, and a 16 bits of data DQ.

A crock buffer 101 is inputted the clock enable signal CKE and the clocksignal CLK, and buffers and outputs the clock signal CLK to each ofother circuit blocks. A circuit 102 includes a command buffer, a latch,and a decoder; and is inputted the chip select signal /CS, the rowaddress strobe signal /RAS, the column address strobe signal /CAS, andthe write enable signal /WE, and buffers, latches, and decodes thesesignals. With the combination of these signals being decoded, a commandcan be obtained. The command includes, for example, an active command, aprecharge command, a read command, a write command, and the like. Thecommand is outputted to a control signal generator 105.

A circuit 103 includes an address buffer and a latch, buffers andlatches the bank address BA and the address A, and then outputs them tothe control signal generator 105, a DRAM core 107, and a column addresscounter 106. The column address counter 106 increments the columnaddress inputted from the bit line 103 in order and outputs a columnaddress CA to the DRAM core 107. The control signal generator 105generates and outputs a control signal CTL, a four bits of active banksignal “active_bankz”, and an output enable signal “oenz”.

A circuit 104 that includes a buffer and a latch is inputted the activebank signal “active_bankz” and the output enable signal “oenz”, andbuffers and latches the data DQ and the data mask signal DQM to output adata “dqz” and a data mask signal “dqmz” to the DRAM core 107. Thecircuit 104 will be detailed hereinafter with reference to FIG. 2. Theterminal for the data DQ is a terminal being inputted a write data fromoutside to output a read data outside.

The DRAM core 107 is a memory cell array having for example four banks“bank 0” to “bank 3”; and is inputted the control signal CTL, the activebank signal “active_bankz”, a row address RA, the column address CA, andthe data mask signal “dqmz”, and inputs and outputs the data “dqz”.

FIG. 2 is a circuit diagram showing a configuration example of thecircuit 104 in FIG. 1. An input buffer 201 is inputted the two bits ofdata mask signal DQM from outside, and buffers and outputs the same to aflip-flop 204. An input buffer 202 is inputted the 16 bits of write dataDQ from outside, and buffers and outputs the same to a flip-flop 205.The input buffer 203 is inputted the clock signal CLK from outside, andbuffers and outputs the same.

Inverters 211, 212 configure a buffer to amplify an output signal of aninput buffer 203 and output a clock signal “clkmz”.

A negative logical sum (NOR) circuit 215 and three inverters 216 to 218configure a logical sum (OR) circuit. The NOR circuit 215 is inputtedfour bits of four active bank signals “active-bankz <0>” to“active-bankz <3>”. An output signal “dienz” of the inverter 218 is anOR signal of the four bits of active bank signals “active-bankz <0>” to“active-bankz <3>”.

A negative AND (NAND) circuit 213 and an inverter 214 configure alogical multiplication (AND) circuit. The NAND circuit 213 is inputtedthe output signal of the input buffer 203 and the signal “dienz”. Anoutput signal “clkqz” of the inverter 214 is an AND signal of the outputsignal of the input buffer 203 and the signal “dienz”.

The signal “dienz” indicates an active state when it is at high leveland an inactive state when it is at low level. When the output signal“dienz” is at high level, the clock signal “clkqz” comes to be the samesignal as the output signal of the input buffer 203. When the signal“dienz” is at low level, the clock signal “clkqz” remains to be at lowlevel to be halted.

Further, when the activation signal “dienz” is at high level, the inputbuffer 202 comes into an active state to buffer the write data DQ, butwhen the activation signal is at low level, the input buffer 202 comesinto an inactive state not to buffer the write data DQ. Accordingly, byputting the input buffer 202 into an inactive state, current consumption(power consumption) can be reduced.

The flip-flop (latch circuit) 204 latches the two bits of data masksignal DQM outputted by the input buffer 201 in synchronization with therising output signal “dienz” to output the two bits of data mask signal“dqmz”.

The flip-flop 205 (latch circuit) latches the 16 bits of write data DQoutputted by the input buffer 202 in synchronization with the risingclock signal “clkqz” to output the 16 bits of write data “dqz”. Thewrite data “dqz” is written into the DRAM core 107. When the clocksignal “clkqz” is halted, the flip-flop 205 does not operate, so thatcurrent consumption can be reduced.

A read data read out from the DRAM core 107 is outputted to the terminalfor the data DQ without passing through the input buffer 202 and theflip-flop 205. The input buffer 202 and the flip-flop 205 are not usedin the read operation but used only in the write operation. Accordingly,preferably, in the write operation, the activation signal “dienz” isbrought into high level to put the input buffer 202 and the flip-flop205 into an active state, and in the read operation, the activationsignal “dienz” is brought into low level to put the input buffer 202 andthe flip-flop 205 into an inactive state. Backed by this, currentconsumption can be reduced.

However, practically, it is difficult to put them into an inactive statein the read operation. Therefore, as shown in FIG. 2, when all of theactive bank signals “active_bankz <0>” to “active_bankz <3>” are in aninactive state (precharge state), the signal “dienz” is brought into lowlevel to thereby put the input buffer 202 and flip-flop 205 into aninactive state. In other words, the input buffer 202 and the flip-flop205 are in an active state at the read and write operation. The reasonthereof will be described hereinbelow with reference to FIG. 3 and FIG.4.

The active signal “active_bankz <0>” is an active state signal of thebank “bank 0”, and comes into high level by an active command and comesinto low level by a precharge command. When inputting the active commandand the precharge command, the bank address BA is set to 0 (zero). Afterthe bank “bank 0” is put into an active state, the read operation by theread command or the write operation by the write command is enabled.Similarly, the active bank signals “active_bankz <1>” to “active_bankz<3>” are the active state signals of the banks “bank 1” to “bank 3”.

FIG. 3 is a timing chart showing a read operation example of the circuitin FIG. 2. When conducting a read operation, an active command ACTV isinputted from outside, and a read command READ is inputted thereafter.

The active command ACTV is inputted from outside together with the bankaddress BA and the address (row address) A. Backed by this, the activebank signal “active_bankz” corresponding to the bank address BA comes tohigh level to put the bank into an active state. For instance, when thebank address BA is 0 (zero), then the active bank signal “active_bankz<0>” comes to high level to put the bank “bank 0” into an active state.Accordingly, the activation signal “dienz” comes to high level to putthe input buffer 202 and the clock signal for latch “clkqz” into anactive state.

Note that, before inputting the active command ACTV, all of the activebank signals “active_bankz <0>” to “active_bankz <3>” are at low level,the activation signal “dienz” is at low level, and the input buffer 202and the clock signal for latch “clkqz” (flip-flop 205) are in aninactive state.

Subsequently, the read command READ is inputted from outside togetherwith the bank address BA and the address (column address) A. Forinstance, when the bank address BA is set to 0 (zero), in the bank “bank0” being in an active state caused by the active command ACTV, it ispossible to read out data Q0 to Q7 from the row address and the columnaddress of the DRAM core 107 that are designated by the active commandACTV and the read command READ. A burst length is for example eight, anda burst read is conducted for eight data of consecutive addresses.

An output enable signal “oenz” comes to high level when outputting dataat the following clock, and comes to low level when putting the terminalof the data DQ into a high-impedance state at the following clock.

The two bits of data mask signals DQM remains to be at low level in boththe cases in normal read operation. Accordingly, the data mask signal“dqmz” also remains to be at low level.

As described above, when all the active bank signals “active_bankz <0>”to “active_bankz <3>” are at low level, the activation signal “dienz”stays at low level, so that the input buffer 202 and the clock signalfor latch “clkqz” (flip-flop 205) come into an inactive state. When atleast one active bank signal “active_bankz” is brought into high levelby the active command ACTV, the activation signal “dienz” comes to highlevel to put the input buffer 202 and the clock signal for latch “clkqz”(flip-flop 205) into an active state.

FIG. 4 is a timing chart showing an example of a write interruptoperation during the burst read of the circuit in FIG. 2. For conductingthis operation, the active command ACTV is inputted from outside, theread command READ is inputted thereafter, and after that, a writecommand WRIT is inputted.

Until a data Q1 is read out, the description is the same as the abovedescription for FIG. 3. After that, the two bits of data mask signal DQMis put into high level in both the cases to generate a high-impedanceperiod Th. In order to write a data D0 by the write command WRIT afterreading data Q0 to Q3 out by the read command READ, the terminal for thedata DQ needs to be brought into a high-impedance state in the period Ththerebetween. Backed by this, at a single data DQ terminal, theswitching from data output to data input is enabled, so that thecontention caused by the input data and the output data can beprevented.

The flip-flop 204 latches the data mask signal DQM in synchronizationwith the rising clock signal CLK to output the data mask signal “dqmz”.When the data mask signal “dqmz” comes into high level, the data Q3 isread out at the following clock, and the terminal for the data DQ comesinto a high-impedance state thereafter.

Note that, in the case of the write operation, the two bits of data masksignal DQM is used to mask an upper byte or a lower byte to therebywrite a write data.

Under normal conditions, with the read command READ, a burst read isconducted to eight data, however, there is sometimes a case where thedata mask signal DQM is brought into high level to thereby input thewrite command WRIT in the course of the read operation. The writecommand WRIT is inputted from outside together with the write data D0(DQ), the bank address BA, and the address (column address) A. Forinstance, when the bank address BA is set to 0 (zero), in the bank 0being in an active state caused by the active command ACTV, it ispossible to write the data D0 into the row address and the columnaddress of the DRAM core 107 that are designated by the active commandACTV and the write command WRIT.

As described above, in the course of the read operation by the readcommand READ, the write command WRIT is inputted sometimes. In the writeoperation by the write command WRIT, the input buffer 202 and theflip-flop 205 are used. Therefore, there may be a case where theoperation is switched to the write operation even in the mid-course ofthe read operation, so that the input buffer 202 and the clock signalfor latch “clkqz” (flip-flop 205) need to be in an active state.Specifically, the write data D0 is inputted together with the writecommand WRIT, thereby the input buffer 202 and the clock signal forlatch “clkqz” (flip-flop 205) need to be in an active state in advancein the read operation before the write command WRIT is inputted. For thereason as described above, the input buffer 202 and the clock signal forlatch “clkqz” (flip-flop 205) are required to be in an active state evenin the normal read operation in FIG. 3.

For the purpose of supporting the write interrupt operation during theburst read, the input buffer 202 and the clock signal for latch “clkqz”(flip-flop 205) are put into an active state even though they are notnecessary to be activated during the normal read operation, so that theSDRAM consumes current wastefully in the read operation, disturbing tolower current consumption. Notwithstanding the above, should the writeinterrupt operation during the burst read be prohibited or should thespecification be modified to input the write data D0 in retard of theinput of the write command WRIT, the existing design assets such as of aSDRAM controller becomes unavailable to finally increase burden onsystem designers.

Subsequently, a method that brings a solution to the above-describedproblems and that reduces current consumption, where the input buffer202 and the clock signal for latch “clkqz” (flip-flop 205) are put intoan inactive state in the mid-course of the read operation withoutmodifying an operation specification, will be described with referenceto FIG. 5 to FIG. 7.

FIG. 5 is a circuit diagram showing a configuration example of thecircuit 104 in FIG. 1 according to one embodiment of the presentinvention. FIG. 5 and FIG. 2 are the same other than the circuit togenerate an activation signal “dienz”.

A NOR circuit 501 and an inverter 502 configure an OR circuit. The NORcircuit 501 is inputted active bank signals “active_bankz <0>” to“active_bankz <3>”. The output signals of the inverter 502 are ORsignals of the active bank signals “active_bankz <0>” to “active_bankz<3>”.

A NAND circuit 503 is inputted “dqmz <0>” and “dqmz <1>” outputted fromthe flip-flop 204 to output their NAND signal. A NAND circuit 504 isinputted the output signal of the NAND circuit 503 and an output enablesignal “oenz” to output their NAND signal.

A NAND circuit 505 and an inverter 506 configure an AND circuit. TheNAND circuit 505 is inputted the output signals of the inverter 502 andthe NAND circuit 504. The activation signal “dienz” outputted from theinverter 506 is an AND signal of the output signals of the inverter 502and the NAND circuit 504.

Specifically, when at least one of the active bank signals “active_bankz<0>” to “active_bankz <3>” is at high level, neither the data masksignal “dqmz <0>” nor the data mask signal “dqmz <1>” is at high level,and the output enable signal “oenz” is at high level, then theactivation signal “dienz” comes into low level. Also, the activationsignal “dienz” comes into low level when all the active bank signals“active_bankz <0>” to “active_bankz <3>” are at low level. In othercases, the activation signal “dienz” comes into high level.

When the activation signal comes into high level, the input buffer 202and the clock signal for latch “clkqz” (flip-flop 205) come into anactive state. When the activation signal “dienz” comes into low level,the input buffer 202 and the clock signal for latch “clkqz” (flip-flop205) come into an inactive state, so that current consumption can bereduced.

FIG. 6 is a timing chart showing an example of a read operation of thecircuit in FIG. 5. When conducting the read operation, the activecommand ACTV is inputted from outside, and the read command READ isinputted thereafter. The description for the command, the clock signalCKL, the data mask signal DQM, the data DQ, an output enable signal“oenz”, and the data mask signal “dqmz” is the same as of aforementionedFIG. 3. Hereinbelow, the description will be given for the activationsignal “dienz”.

Before being inputted the active command ACTV, active bank signals“active_bankz <0>” to “active_bankz <3>” are all at low level, so thatthe activation signal “dienz” comes into low level. Backed by this, theinput buffer 202 and the clock signal for latch “clkqz” (flip-flop 205)come into an inactive state, so that current consumption can be reduced.

Next, the active command ACTV is inputted from outside together with thebank address BA, then the active bank signal “active_bankz”corresponding to the bank address BA comes into high level, and sincethe output enable signal “oenz” is at low level as well, the activationsignal “dienz” comes into high level.

Subsequently, when the read command READ is inputted, as in the case ofthe above-described FIG. 3, the output enable signal “oenz” comes intohigh level. Then, both the data mask signals “dqmz <0>” and “dqmz <1>”are at low level. Accordingly, in a read period Td, the activationsignal “dienz” comes into low level. In the read operation, the inputbuffer 202 and the flip-flop 205 are unnecessary, so that currentconsumption can be reduced by putting the input buffer 202 and the clocksignal for latch “clkqz” (flip-flop 205) into an inactive state.

When a data Q6 is read out thereafter, the output enable signal “oenz”comes into low level. Then, the activation signal “dienz” comes intohigh level. After a data Q7 being the last data is read out, theterminal for the data DQ comes into a high-impedance state. The inputbuffer 202 and the clock signal for latch “clkqz” (flip-flop 205) comeinto an active state, so that preparation for the following writeoperation can be made.

As described above, in the read period Td, the input buffer 202 and theclock signal for latch “clkqz” (flip-flop 205) can be put into aninactive state, so that current consumption can be reduced.

Note that, by inputting a precharge command from outside together withthe bank address BA, the active bank signal “active_bankz” correspondingto the bank address BA can be brought into low level. When all theactive bank signals “active_bankz <0>” to “active_bankz <3>” are putinto low level, the activation signal “dienz” comes into low level, sothat the input buffer 202 and the clock signal for latch “clkqz”(flip-flop 205) can be put into an inactive state.

FIG. 7 is a timing chart showing an example of the write interruptoperation during the burst read of the circuit in FIG. 5. Whenconducting this operation, the active command ACTV is inputted fromoutside, the read command READ is inputted thereafter, and after that,the write command WRIT is inputted. The description for the command, theclock signal CKL, the data mask DQM, the data DQ, the output enablesignal “oenz”, and the data mask signal “dqmz” is the same as ofaforementioned FIG. 4. Hereinbelow, the description will be given forthe activation signal “dienz”.

Before being inputted the active command ACTV, the active bank signals“active_bankz <0>” to “active_bankz <3>” are all at low level, so thatthe activation signal “dienz” comes into low level. Backed by this, theinput buffer 202 and the clock signal for latch “clkqz” (flip-flop 205)come into an inactive state, so that current consumption can be reduced.

Next, the active command ACTV is inputted from outside together with thebank address BA, then the active bank signal “active_bankz”corresponding to the bank address BA comes into high level, and sincethe output enable signal “oenz” is at low level as well, the activationsignal “dienz” comes into high level.

Subsequently, when the read command READ is inputted, as in the case ofthe above-mentioned description for FIG. 4, the output enable signal“oenz” comes into high level. Then, both the data mask signals “dqmz<0>” and “dqmz <1>” are at low level. Accordingly, in the read periodTd, the activation signal “dienz” comes into low level. In the readoperation, the input buffer 202 and the flip-flop 205 are unnecessary,so that current consumption can be reduced by putting the input buffer202 and the clock signal for latch “clkqz” (flip-flop 205) into aninactive state.

Subsequently, before inputting a next write command WRIT, the read datamask signals DQM <0> and DQM <1> are put into high level. The read datamask signals “dqmz <0>” and “dgmz <1>” come into high level in the samemanner in synchronization with the following rising clock signal CLK.Then, the activation signal “dienz” comes into high level, and the inputbuffer 202 and the clock signal for latch “clkqz” (flip-flop 205) comeinto an active state. In the high-impedance period Th, the terminal forthe data DQ comes into a high-impedance state in response to the highlevel of the data mask signals “dqmz <0>” and “dqmz <1>”.

Subsequently, the write command WRIT is inputted from outside togetherwith the write data D0. Since the input buffer 202 and the clock signalfor latch “clkqz” (flip-flop 205) are at low level at that time, thewrite data D0 is buffered by the input buffer 202 to be latched by theflip-flop 205. After that, the write data D0 is written into a memorycell normally.

As describe above, in the read period Td, the input buffer 202 and theclock signal for latch “clkqz” (flip-flop 205) can be put into aninactive state, so that current consumption can be reduced. Wheninputting the write command WRIT, the activation signal “dienz” is athigh level and the input buffer 202 and the clock signal for latch“clkqz” (flip-flop 205) are in an active state, allowing a normal writeoperation.

As has been describe in the above, in the present embodiment, whenconducting a writeinterrupt operation during a burst read, for thepurpose of preventing the contention caused by the input and output dataDQ, a mask function of a read data using a read data mask signal DQM isemployed. During a read operation, the input buffer 202 and the clocksignal for latch “clkqz” (flip-flop 205) are put into an inactive state,however, when the mask function of the read data is used, the inputbuffer 202 and the clock signal for latch “clkqz” (flip-flop 205) areput back into an active state to prepare for the input of the writecommand WRIT.

Concretely, when all banks are in a precharge state, an activationsignal “dienz” comes into low level, so that the input buffer 202 andthe clock signal for latch “clkqz” (flip-flop 205) come into an inactivestate. However, when any of the banks is in an active state, theactivation signal “dienz” comes into high level, so that the inputbuffer 202 and the clock signal for latch “clkqz” (flip-flop 205) comeinto an active state. When it is in the read operation (the outputenable signal “oenz” is at high level) even if any of the banks is in anactive state, the activation signal comes into low level and the inputbuffer 202 and the clock signal for latch “clkqz” (flip-flop 205) comeinto an inactive state. Even if it is in the read operation (the outputenable signal “oenz” is at high level), when the mask function of theread data is employed (the data mask signals “dqmz <0>” and “dqmz <1>”are at high level), the activation signal “dienz” comes into high level,so that the input buffer 202 and the clock signal for latch “clkqz”(flip-flop 205) come into an active state.

The input buffer 202 and the clock signal for latch “clkqz” (flip-flop205) can be halted even in the state of a burst read without modifyingthe operation specification concerning a write data and the input timingof the write data while still supporting an operation of interrupting aburst read of a SDRAM with a write command, so that a SDRAM of a lowcurrent consumption can be provided without increasing burden on systemdesigners.

In should be noted that any of the above-described embodiments aremerely concrete examples to implement the present invention, and it isto be understood that the technical scope of the present invention willnot be construed restrictive by these embodiments. In other words, thepresent invention can be realized in various forms without departingfrom the technological spirit and the main features thereof.

Current consumption can be reduced by putting into an inactive stateduring a read operation, and also, by putting into an active statecorresponding to a read data mask signal, a write operation after theread operation can be conducted normally.

The present embodiments are to be considered in all respects asillustrative and no restrictive, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein. The invention may be embodied in other specificforms without departing from the spirit or essential characteristicsthereof.

1-10. (canceled)
 11. A semiconductor memory device comprising: a controlcircuit putting a clock signal for latch into an inactive state during aread operation and putting the clock signal for latch into an activestate when a read data mask signal is inputted thereafter; and a latchcircuit to latch a write data inputted from outside in synchronizationwith the clock signal for latch.
 12. The semiconductor memory deviceaccording to claim 11, further comprising a data terminal inputting thewrite data from outside to output a read data outside, wherein the readdata mask signal is a signal to put said data terminal into ahigh-impedance state.
 13. The semiconductor memory device according toclaim 12, wherein said latch circuit latches the write data inputtedfrom outside together with a write command, after said data terminalcomes into a high-impedance state.
 14. The semiconductor memory deviceaccording to claim 13, wherein said control circuit puts the clocksignal for latch into an inactive state when a read command is inputtedfrom outside.
 15. The semiconductor memory device according to claim 14,wherein said control circuit puts the clock signal for latch into aninactive state when an output enable signal in response to the input ofthe read command is inputted.
 16. The semiconductor memory deviceaccording to claim 14,